Melanomas are typically resistant to a variety of chemotherapeutic agents. While the basis for chemoresistance of a number of neoplasms is generally understood, the mechanisms leading to melanoma chemoresistance are unclear. Moreover, sensitivity of melanocytes to cytotoxic insult has been implicated in the pathogenesis of vitiligo. Recently, the melanocyte-specific pink-eyed dilution (p) gene product has been implicated in controlling melanocyte sensitivity to cytotoxic compounds including arsenicals and cisplatin. Melanocytes from mice with a deletion of this gene are resistant to these agents and expression of the p gene in yeast leads to increased sensitivity to arsenical compounds and other metalloids. The availability of small molecules to dissect the operative pathways controlling the sensitivity of melanocytic cells to cytotoxic agents would be of value to basic researchers as well as offering potential therapeutic leads. A systems-based "chemical genetics" approach is proposed to further understanding of the pathways controlling these processes. Specific aims of the proposed research are: 1. Screening of a diverse triazine-based tagged library of 10,000 compounds in a simple cytotoxicity assay that will identify those compounds not inherently cytotoxic but capable of overcoming the resistance of melanocytes lacking p gene expression to arsenic and cisplatin. 2. Combinatorial chemistry to maximize the potency of lead compounds and to define structural requirements for activity. 3. Isolation of cellular targets for active compounds by affinity chromatography using immobilized compound. The molecules in this unique library all contain one of several long linkers at one of 3 R positions, allowing the construction of affinity matrices to rapidly isolate the targets of the lead compounds. Microsequencing of affinity-isolated targets will be performed and used to identify targets from protein databases. Findings from the proposed studies will result in a deeper understanding of the cellular pathways underlying melanocyte chemosensitivity, and in new research tools for cell biologists. The data should provide the basis for future therapeutics to treat metastatic melanoma and for purposes of depigmentation.